Catalytic Decomposition Of Nitrous Oxide Over Supported Transition Metal Catalysts On Oxide

Nitrous oxide is the third largest greenhouse gas,seriously damage the ozone layer,harm human health,and can be stable in the atmosphere,so its emission reduction is of great significance.The supported transition metal oxide catalysts are widely used in the direct catalytic decomposition of nitrous oxide due to low cost,high activity and good thermal stability,and have good industrial application prospects.In this paper,seven kinds of common oxide carriers were used to prepare supported cobalt-based catalysts by equal volume impregnation method for the study of direct catalytic decomposition of nitrous oxide.The performance differences of catalysts prepared by different carriers were investigated.Through activity evaluation and characterization,it was found that the catalysts prepared with ZnO,ZrO₂and CeO₂as support had high catalytic activity.When ZnO was used as the carrier to prepare the catalyst,the best active component was transition metal oxide Co₃O₄.With the increase of Co₃O₄ loading,the catalyst activity first increased and then decreased.When the loading was 14%（w%）,the catalyst activity was the highest.The performance of catalysts prepared by different methods was compared.The results showed that the catalyst prepared by equal volume impregnation method had the best activity.Based on the above results,after the addition of the second active component transition metals（Cr,Mn,Fe,Ni,Cu）,rare earth metals（La,Ce,Nd,Y）,alkali metal K and alkali-earth metal Mg oxides,the activity of the catalysts decreased to varying degrees.The best calcination temperature of Co/ZnO catalyst is 460°C and the best calcination time is 2 h.When ZrO₂ was used as the carrier to prepare the catalyst,the best active component was transition metal oxide Co₃O₄.With the increase of Co₃O₄ loading,the catalyst activity first increased and then decreased.When the loading was 14%,the catalyst activity was the highest.Based on the above results,after adding Mn oxides,the XRD characterization results showed that the dispersion of Co₃O₄ was improved,and the activity of the catalyst was significantly improved.The optimum calcination temperature of Co Mn/ZrO₂ Catalyst is 550℃and the optimum calcination time is 4 h.When CeO₂ was used as the support to prepare the catalyst,the best active component was Ni O,followed by Co₃O₄.The optimal loading of Ni O was 12%.After the addition of the second component of transition metals（Cu,Co,Fe,Mn,Ag,Zn）,rare earth metals（La,Nd）,alkali metal K and alkali-earth metal Mg oxides,the catalyst activity decreased to varying degrees.The optimal loading of Co₃O₄ was 14%,and the activity of the catalyst was significantly improved after the addition of the second active component La oxide.The optimum loading of La is 2%,the optimum calcination temperature is 550℃,and the optimum calcination time is 4 h.The orthogonal experiment with three factors and four levels was designed to investigate the synergistic effect of Co,La and Mn with CeO₂ as the carrier.The results showed that the catalyst activity decreased when La and Mn were added to Co/CeO₂ at the same time,so there was no synergistic effect among Co,La and Mn.Based on the background of industrial application,orthogonal experiments were designed to investigate the influence of forming conditions on the performance of Co La/CeO₂ catalyst.The results showed that the amount of pseudoboehmite had the greatest influence on the mechanical strength of Co La/CeO₂ catalyst,followed by the water powder ratio,the concentration of nitric acid and the content of sesbania powder.The activity of the molded catalyst was lower than that of the laboratory catalyst.The activity of Co La/CeO₂ catalyst decreased with the increase of the amount of pseudo-boehmite,but the concentration of nitric acid,water powder ratio and the content of sesbania powder had no effect on the activity of the catalyst.